A computational method for post-construction settlement of high-speed railway bridge pile foundation considering soil creep effect

Based on reasonable assumptions that simplified the calculational model,a simple and practical method was proposed to calculate the post-construction settlement of high-speed railway bridge pile foundation by using the Mesri creep model to describe the soil characteristics and the Mindlin-Geddes method considering pile diameter to calculate the vertical additional stress of pile bottom.A program named CPPS was designed for this method to calculate the post-construction settlement of a high-speed railway bridge pile foundation.The result indicates that the post-construction settlement in 100 years meets the requirements of the engineering specifications,and in the first two decades,the post-construction settlement is about 80% of its total settlement,while the settlement in the rest eighty years tends to be stable.Compared with the measured settlement after laying railway tracks,the calculational result is closed to that of the measured,and the results are conservative with a high computational accuracy.It is noted that the method can be used to calculate the post-construction settlement for the preliminary design of high-speed railway bridge pile foundation.

Secondary settlement estimation in surcharge preload subject to time effect of secondary consolidation coefficient

In order to eliminate the settlement underestimation in surcharge preload engineering, a study based on Bjerrum's creep diagram and the tangent slope definition of secondary consolidation coefficient was carried out to analyze the time effect of secondary consolidation coefficient of over consolidated soil, and a time–growth model for it was formulated. As Bjerrum's creep diagram is an idealized model, oedometer tests were performed to improve the above time–growth model of secondary consolidation coefficient for the purpose of achieving a better agreement with the actual ground situations. It is found that secondary consolidation coefficient of over consolidated soil not only decreases with the ratio of historical maximum to current effective stress of soil(OCR), but also increases with the development time of secondary consolidation. No matter how large OCR is, the long-term time effect of secondary consolidation coefficient of over consolidated soil is all significant. Based on the above results, a model for settlement estimation was formulated and a case study to estimate it indicates that the settlement estimated by our method is 2–5 times larger than that estimated by the previous method. Moreover, the larger the OCR is as well as the longer the service life is, the larger the difference between our method and the previous method is. Thus, the post-construction secondary settlement in surcharge preload engineering will be underestimated when neglecting the time effect of secondary consolidation coefficient in over consolidated state.

低路堤桩-筏复合地基沉降超限治理措施研究

依托某高速铁路低路堤桩-筏复合地基工程背景,在分析运营期路基沉降超限原因的基础上,充分考虑场地、设备及天窗施工等限制条件,提出一套低路堤桩-筏地基沉降超限处治技术措施,主要包括:路基坡脚处设置应力释放孔、路基底部花管注浆加固、更换垫块及抬高扣件.同时,结合处治前后实测沉降数据对处治效果进行评估.

电力工程建设项目超概分析及对策探讨

指出了电力建设项目超概的原因有决策阶段投入不够、投资估算误差大、项目设计审查不严等。探讨了在保证工程项目质量标准的前提下,力求合理使用人力、财力、物力,通过优化设计、加强施工管理、控制预算外支出、加强结算管理等措施控制工程造价。

Experimental Study on Improvement Effects of Completely Weathered Phyllite Using Red Clay and Cement for High-Speed Railway Embankments

Completely weathered phyllite(CWP)has the characteristics of difficult compaction,low shear strength after compaction and large settlement after construction.The traditional improvement method using a single agent of red clay or cement for CWP satisfies the subgrade requirements for ordinary railway,but cannot meet the requirements of immediate strength and long-term post-construction settlement of high-speed railway at the same time.A series of experimental investigations were undertaken for the blended CWP soils,with three additives used.The first additive was red clay,the second was cement and the third was a combination of both red clay and cement at various portions.Results of consolidation test and shear strength test carried out for the treated CWP soils show that:1)The effect of cement on improving the compression modulus of CWP is much better than that of red clay;2)The settlement of an embankment of 10 m high formed by blended soil of CWP with 3%cement can be controlled within 15 mm,while the settlement will be 25.15 mm for the same embankment of blended soil of CWP with 40%red clay;3)The shear strength and ultimate bearing capacity of CWP improved by red clay are much better than those of 5%cement;4)The ultimate bearing capacity of CWP improved by 40%red clay is 3.42 times of that by 3%cement and 2.95 times by 5%cement.Furthermore,the bearing capacity of CWP when improved by red clay can meet railway subgrade requirements immediately after compaction,while cement improved CWP needs a curing time of 1 day or longer.This is an impediment to rapid construction process.The improvement mechanism of red clay is mainly filling effect and grading improvement effect,while the improvement mechanism of cement is mainly hardening reaction,which produces high strength material to cement.It is found that 40%red clay and 3%cement treated CWP,which is considered to be optimum,can meet the subgrade requirements of both immediate bearing capacity and long-term post-construction settlement for the high-speed railway.

基于灰色关联分析的政府投资项目竣工结算超支因素研究

本文首先介绍了政府投资项目竣工结算超支现状;其次引用已完成的案例数据,采用灰色关联分析模型对影响结算超支因素进行排序,得出竣工结算超支的最大影响因素。为政府投资项目管理者在实际工程管理中作为投资控制的参考,提高政府投资的效用,进而提高政府的公信力。

下穿107国道盾构施工关键技术研究

通过分析深圳地铁下穿107国道施工可能遇到的问题,介绍了盾构机安全顺利通过的合理掘进参数,总结出盾构法隧道下穿道路施工的关键技术措施,这些成功经验都可为日后深圳乃至其他城市类似工程提供参考和借鉴。